This application is based upon and claims benefit of priority of Japanese Patent Application No. 2001-268168 filed on Sep. 5, 2001, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a starter motor for cranking an internal combustion engine, the starter motor having a planetary gear device for reducing a rotational speed of an electric motor.
2. Description of Related Art
An example of conventional starter motors of this kind is disclosed in JP-B2-3158514. The starter motor disclosed therein includes a planetary gear device for reducing a rotational speed of an electric motor and a shock-absorbing device for absorbing an excessive impact applied to the planetary gear device from an internal combustion engine. The planetary gear device includes an annular member, on an inner surface of which an internal gear is formed. The annular member is connected to a rotatable disc of the shock-absorbing device so that the annular member rotates together with the rotatable disc to absorb an excessive impact applied to the starter motor.
The electric motor is separated from the planetary gear device by a separating plate to prevent lubricant supplied to the planetary gear device from flowing into an electric motor chamber. The separating plate also serves to prevent brush dusts of the electric motor from entering into the planetary gear device. The separating plate contacts an axial end surface of a cylindrical portion of the annular member, so that the annular member rotates together with the rotatable disc relative to the separating wall to absorb an excessive impact applied to the starter motor from the internal combustion engine. Because of the relative rotation between the annular member and the separating plate, abrasion wear occurs on the axial end surface of the cylindrical portion. Accordingly, it is highly possible that brush dusts generated in the electric motor chamber enter into the planetary gear device, causing malfunction in gear engagement and generating noises.
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved starter motor, in which the abrasion between the separating plate and the annular member is suppressed, and thereby the brush dusts are prevented from entering into the planetary gear device.
The starter motor for cranking an internal combustion engine is composed of an electric motor, a planetary gear device, a one-way clutch, an electromagnetic switch. The planetary gear device is composed of a sun gear driven the electric motor, an internal gear and planetary gears engaging with the sun gear and the internal gear. A rotational speed of the electric motor is reduced by the planetary gear device, and a tortational torque is transmitted to an pinion that drives a ring gear of the engine through the one-way clutch. The one-way clutch transmits the rotational torque to the pinion, while intercepting transmission of a rotational torque from the engine to the starter motor. Electric power is supplied to the electric motor through the electromagnetic switch, and the pinion is shifted to a position to engage with the ring gear by a lever driven by the electromagnetic switch. The starter motor also includes a shock-absorbing device that absorbs an excessive impact transmitted from the engine to the starter motor.
The planetary gear device and the shock-absorbing device are housed in a center case and separated from the electric motor by a separating plate. The planetary gear device includes an annular member having a cylindrical portion, on an inner surface of which the internal gear is formed. The annular member made of a material such as resin is inserted into the center case so that the annular member rotates relative to the center case when an excessive impact is transmitted from the engine to the starter motor through the planetary gear device, thereby absorbing the excessive impact. An axial end surface of the cylindrical portion contacts the separating plate. If the axial end surface wears by abrasion with the separating plate, foreign particles such as brush dusts enter the planetary gear device thereby causing malfunction in gear engagement in the planetary gear device and generating harmful noises.
In order to suppress the abrasion wear of the axial end surface of the cylindrical portion, a depressed portion in which lubricant supplied to the planetary gear device is retained is formed on the axial end surface. The axial end surface rotatable relative to the separating plate is properly lubricated by the lubricant retained in the depressed portion, and thereby the abrasion wear is suppressed. The depressed portion also serves to keep the foreign particles therein to prevent them from entering into the planetary gear device.
The depressed portion may be variously shaped. It may be a continuous circular groove or more than two circular grooves formed coaxially to one another. The circular groove may include widened portions to retain more lubricant therein. A continuous groove may be made along an outline of the internal gear teeth. Plural discrete grooves may be formed on the axial end surface. The depressed portion or the groove may be formed on the separating plate in an area contacting the axial end surface instead of forming it on the axial end surface.
According to the present invention, the abrasion wear of the axial end surface of the cylindrical portion are suppressed by the lubricant retained in the depressed portion, and thereby foreign particles such as brush dusts are prevented from entering the planetary gear device.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.